1. Field of the Invention
The present invention relates to a bulb socket and, in particular, to a socket for a wedge base bulb (no-cap bulb) for use in an automotive lighting device or the like.
2. Related Art
A conventional bulb socket, as shown in FIG. 16, comprises a socket main body 2 which is formed of synthetic resin and includes a bulb insertion opening 3. The bulb insertion opening 3 is opened forwardly and is capable of receiving a wedge base bulb 5. Within the bulb insertion opening 3 are provided a plurality of contact terminals 4 formed of metal. Each of the contact terminals includes a tongue-piece-shaped is contact hold piece 4a and a tongue-piece-shaped bulb securing piece 4b respectively formed integrally therewith. An electricity supply wire 8 is connected to each of the contact terminals 4.
In this structure, the bulb 5 can be inserted into the bulb insertion opening 3 from above and removed from the bulb insertion opening 3, by means of the elasticity of the contact terminals (bulb securing pieces 4b).
That is, when the wedge base bulb 5 is inserted into the bulb insertion opening 3, the projection 6a of the base portion 6 of the wedge base bulb 5 is engaged with the bulb securing pieces 4b to thereby prevent the bulb 5 from being removed and, at the same time, the contact hold pieces 4a are contacted with a lead wire 7 of the bulb exposed on the surface of the base portion 6 to thereby connect the filaments 5a and 5b of the bulb 5 with the contact terminals 4 electrically.
However, in the above-mentioned conventional bulb socket, the bulb securing pieces 4b of the contact terminals 4 are too low in flexibility, which makes it difficult to insert and remove the bulb 5 with respect to the bulb insertion opening 3. The present inventors have studied the conventional bulb socket and have found the following discoveries.
That is, the contact terminals 4 are disposed in such a manner that they are in close proximity to the inside of the forming wall 3a of the bulb insertion opening 3, while the bulb securing pieces 4b are also extended in such a manner that they are in close proximity to the bulb insertion opening forming wall 3a. Due to this, when the bulb 5 is inserted into or removed from the bulb insertion opening 3, the bulb securing pieces 4b cannot be elastically deformed in an outward direction (in a direction to spread the bulb insertion opening 3) smoothly, which provides an obstacle to the easy insertion and removal of the bulb 5.
In view of this, the present inventors have tried to separate the bulb securing pieces 4b of the contact terminals 4 from the bulb insertion opening forming wall 3a, with the result that the bulb securing pieces 4b can be elastically deformed smoothly with the insertion of the bulb 5 and the bulb 5 can be thereby inserted and removed easily.
However, in this experiment, although the easy insertion and removal of the bulb 5 is made possible, since the spring forces of the bulb securing pieces 4b are weak, if the insertion and removal of the bulb 5 are repeated, then there arises a new problem that the bulb securing pieces 4b can be easily weakened or the bulb 5 can be removed unexpectedly.
To solve this new problem, the present inventors have conducted another experiment in which, as a member for supporting the bulb securing pieces 4b, a vertical wall-like cantilever beam is so disposed in the rear of the bulb securing pieces 4b as to extend along the bulb securing pieces 4b. As a result of this experiment, the present inventors have confirmed that not only the bulb 5 can be inserted easily but also the weakening of the bulb securing pieces 4b and the removal of the bulb 5 can be prevented effectively. This is the reason why the inventors have decided to propose the present invention.